Many of the characters required by each code page are common; for example, the first 128 characters of all the ASCII code pages are identical. This set of characters is called the Universal Glyph List (UGL). A code page is simply a set of pointers into the UGL.
As the characters in every font are in the same order, only one set of code-page translation tables is necessary.
Note: The fonts of Microsoft Windows support only code page 1004.